fix(python): add type casts to fix ty check errors

Add cast() calls for handler results that go through
inspect.isawaitable(), which loses type narrowing:
- session.py: _handle_permission_request, _handle_user_input_request
- client.py: _execute_tool_call

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SteveSandersonMS

python/copilot/client.py

@@ -1589,7 +1589,7 @@ async def _execute_tool_call(
                 toolTelemetry={},
             )
 
-        return self._normalize_tool_result(result)
+        return self._normalize_tool_result(cast(ToolResult, result))
 
     def _normalize_tool_result(self, result: ToolResult) -> ToolResult:
         """

python/copilot/session.py

@@ -8,7 +8,7 @@
 import asyncio
 import inspect
 import threading
-from typing import Any, Callable, Optional
+from typing import Any, Callable, Optional, cast
 
 from .generated.rpc import SessionRpc
 from .generated.session_events import SessionEvent, SessionEventType, session_event_from_dict
@@ -336,7 +336,7 @@ async def _handle_permission_request(
             result = handler(request, {"session_id": self.session_id})
             if inspect.isawaitable(result):
                 result = await result
-            return result
+            return cast(PermissionRequestResult, result)
         except Exception:  # pylint: disable=broad-except
             # Handler failed, deny permission
             return {"kind": "denied-no-approval-rule-and-could-not-request-from-user"}
@@ -388,7 +388,7 @@ async def _handle_user_input_request(self, request: dict) -> UserInputResponse:
             )
             if inspect.isawaitable(result):
                 result = await result
-            return result
+            return cast(UserInputResponse, result)
         except Exception:
             raise